This invention relates to a 1,2-bis(dialkylphosphino) benzene derivative having an optical activity which is suitably useful as a ligand for an asymmetric catalyst for use in asymmetrical hydrogenation, and also to a process for producing such a benzene derivative. Further, the invention relates to a rhodium metal complex containing, as a ligand, such an optically active 1,2-bis-(dialkylphosphino) benzene derivative which is suitable as an asymmetric catalyst for use in asymmetrical hydrogenation.
The development of new chiral phosphine ligands has given a great impetus to studies on asymmetric syntheses using metal catalysts so that these studies have become rapidly progressive over the last 30 years. Most of these ligands are configured so as to have a center of asymmetry on a carbon skeleton, a phosphorus atom bonded to that skeleton and two aryl groups situated on this atom. Meanwhile, little has been studied regarding P-chiral phosphine ligands structured to have dialkyl and trialkyl groups attached thereto. This is due to the fact that the latter ligands are difficult to synthesize.
Recently, the present inventors have proposed a 1,2-bis-(akylmethylphosphino) ethane having a P-chiral trialkyl group and represented by the following general formula (3): ##STR2##
(where R denotes a cyclopentyl, cyclohexyl, tert-butyl, 1,1-diethylpropyl group or 1-adamantile) (J. Am. Chem. Soc., 120, 1635-1636, 1998). The ethane compound noted here permits a variety of .alpha., .beta.-unsaturated .alpha.-amino acids and their esters to be asymmetrically hydrogenated with high efficiency.
Nevertheless there still remains a demand for the development of other phosphine ligands which are optically active and particularly suitable as a ligand for use in an asymmetric catalyst in asymmetrical hydrogenation.
Accordingly, principal objects of the present invention are to provide a 1,2-bis(dialkylphosphino) benzene derivative possessing an optical activity and which is suitably useful as a ligand for an asymmetric catalyst in asymmetrical hydrogenation, a process for producing such a benzene derivative, and a rhodium metal complex containing, as a ligand, such a benzene derivative which is applicable as an asymmetric catalyst in asymmetrical hydrogenation.